Manufacture of metal coated products



Oct. 5, 1937. v N.VE. cooK ET AL MANUTACTURE 0F METAL COATED PRODUCTSFiled Mar'cn 22, 1935.

NWN

Patented Oct. ,5, 1.937

' MANUFACTURE or METAL coA'rED PRODUCTS Nelson E. cook, wheeling, W.va.,.Edwara J.

Knopf, Morristown,

Diehl, Wheeling, W. Va., assignors to'v Wheeling Steel Corporation,Wheeling, W. Va., a corporation of Delaware Application March 22, 1935,Serial NoT 12,398 s claims. (ol. :i1-470.2)

' This invention relates to the manufacture of metal coated products,and; while not specifically so limited, has particular applicationin'the coating, and especially the galvanizing, of sheet metal, such,for example,- as steel sheets. Superior coated products, andparticularly galvanized sheet steel products, are produced. Such prod.

ucts are claimed in our Acopending application Serial No. 54,278filedDecember 13, 1935, which l application is in part a division of thisapplication. This application is in part acontinuation of our copendingapplication Serial No. 741,222,

filed August 24, 1934.

llnirely` for purposes of description and illusfaces are notundesirable, and indeed they are definitely desirable in caseswhere acertain type of finished appearance is Wanted. f

However, for other purposes sheets having both surfaces Spangled aredefinitely undesirable, as, for example, when the product is to bepainted.

Spangledgalvanized surfaces will not take paintlreadily. It has been thepractice' heretofore to permit Spangled galvanized sheets to weather, or

`to artificially weather them, as byv treatment` with acid or otherchemical having the effect of oxidizing the surfaces ofthe sheets,`inorder that the surfaces to be painted may vbecome-some-What roughened sothat paint will readily adhere thereto.

We have discovered that galvanized sheets may 40 be produced without theordinary Spangled surfaces, without the undesirable buckling of thesheets which has attended previous efforts to produce unspangledgalvanized sheets, and with a smooth dull matte lor slightly roughenedsur.- face which is at the same time highly resistant to corrosion,beautiful in appearance and readily receptive to paint and other similarcoating materials. We are well aware of the previous efforts which havebeen made along these lines in ,v both the practical and the patentedart, but no processhaving the features and advantages .of ourprocess hasheretofore been proposed and no nish having the desirable qualities ofour nish has heretofore been produced.

Before proceeding to explain our invention we f as the results obtainedby the two processes are dinary galvanized ware will be produced.` By

'PATENroFFlcE Ohio, and William L.

Wish it understood that we do not claim broadly to have inventedtheformation o'f unspangled galvanized metal surfaces, as unspangledsurfacesA have been produced before. One Way in which unspangled,galvanized 'surfaces have been produced 5 is by dipping the hot,galvanized ware as it comes from the galvanizing pot into a liquid bath,which prevents the formation of spangles,'produces a mottled, irregular,partly bright and partly dull surface and results in warping the waredue to the 10 rapid and uneven temperature changes brought'. about bythe dipping. The warping can be reduced to some lextent by heating thebath in which the ware is dipped, but, aside from the question ofwarping, the nish is unsatisfactory in appearance, isnot highlyresistant to corrosion and will not take paint readily. It has also beenproposed .to subject galvanized ware to the action of a jety .of wateror other liquid, but this has substantially the same results as dipping.Thenish produced is not uniform, being partly bright and partly dull andmottled, is not highly resistant to corrosion and will not take paintsatisfactorily. Furthermore, the subjectlng of the hot galvanized? wareto a jet of liquid results in warping of thev ware as in the case ofdipping. f l l ,"After considerable experimenting we have dlscoveredthat the highly desirable unspangled, uniform, dull matte finish may beproduced by subjecting the galvanized ware (here considered forlpurposes of illustration as comprising sheets) to the action of a mistor very fine spray. The inist or very line sprayis to be clearlydistinguished from the `jet of liquid referred to above,

entirely different. 'Ihe sheets after leaving the galvanizing bath arebrought into the presence of the' mist or very ne spray before the largespangles characteristic of ordinary galvanized ware have formed. Almostimmediately upon leaving the galvanizing bath the zinc coating begins tolcoolandvcrystallization commences. If this crystallization is allowedto progress unhindered the large spangles characteristic of orbringingthe hot sheets into the presence of the mist or very line spray weprevent the formation of the large spangles and the desired uniform dullmatte finish results. i

- While we are not certain as to the` theory underlying the processabove described, we think that the fine particles of the mist exert aphysical effect on the surface of the sheet, creating relatively veryclosely spaced centers of propagaotheri before the `crystals can attainrelatively large size, resulting, as it were, in the squeezing into thesame surface area` of a relatively very great number of relativelyverysmall crystals which, due to the relative proximity of their centersof propagation or crystallization, have had no opportunity to grow toor. even to approach the .size of \what are commonly known as s'pang1es,which are readily distinguishable to the naked eye even at some distanceand which may in some cases extend from their'respective centers ofcrystallization for/'a distance of an inch or more in variousdirections; if the size of the crystals is properly controlled the sheetwill appear to the naked eye to have a uniform continuous dull mattesurface. Underv a powerful magnifying glass this surface will be seen tobe crystalline, presenting an appearance similar to an ordinary Spangledsurface. However, the relatively gr'eat number of relatively small,relatively' closely spaced crystals afords an ideal surfaceV for thereception of paint and similar. coatings, and this surface is alsoparticularly' well suited for various uses without painting or coveringYwith similar coatings, as, for example, for oven linings.

We have found that by lappropriately controlling the mist or sprayandthe passage of the` sheet in relation thereto we can form a 4sheethaving one side Spangled in the characteristic thus produced. Anotheruse to which sheets hav- A ing one side Spangled in the usual manner andthe other side provided with the uniform dull matte iinish'may be put isin the construction of refrigerator cases. The side having the dullmatte finish forms the outside of the case and receives the usualfwhiteenamel paint, while the Spangled side faces toward the interior of therefrigerator and is naturally well adapted to withstand corrosion due tomoisture within the refrigerator. Sheets of this character may also beused for oven linings, the unpainted dull matte nish facing the interiorof the oven.

Various materials may be used for producing the mist or very fine spray.Plain water alone -if sufli'cientlyffinelyv divided is fairlysatisfactory.

Using a fine mist of plain water does not, however, give as. exactcontrol of surface appearance as is ,desirable for manypurposes.However,`we have found that water solutions of certain chei`nicalsproduce markedly superior results.Y A few of .thechemicals thus usedlisted approximately in the order of efficacy are copper sulphate,.

sodium nitrate, sodium chloride, potassium'chromateand potassiumpermanganate. These salts are precipitated rapidly from their watersolutions at temperatures slightly above the solidifying point of zincor the zinc alloys usually employed' for galvanizing. The solidifyingpoint of aceaasa tion or crystallization from which the crystalsy thegalvanizing material `may be in the neighborhood of 760 F. to 800 F.`While we are not certain as to thetheory of action, we believe that therapid evaporation of the water results in the almost immediateprecipitation or deposition on 5 the surface of the. sheet ofmicroscopic, almost unmeasurably small. particles ofthe Salt or of someprecipitate formed upon the application of heat to the` mist composed ofthe salt solution. This precipitate'seems to have the effect of con- 10trolling the centers of propagation of the crystals so that such centersare distributed quiteuniformly over the surface of the sheet and veryclose together. Apparently those substances whose solutions most quicklydeposit their precipitates onthe'sur'face of the sheet upon theapplication of heat in the neighborhood of thetemperatures .mentionedabove are `mostsatisfactory for our purpose.

Care must be taken to keep the mist very finely. divided. If arelatively coarse spray or jetis methods of treatment. of coatedsheetsand certain present preferred-apparatus for carrying out the methodandproducing the desired product proceeds.

, In the accompanying drawing we have shown Acertain present preferredforms of apparatus for producing coated'sheets,`in which Figure 1 is aplan vview of one form 'of apparatusf Figure 2 is an elevational view,partly in ver- 40 tical longitudinal cross section, of the apparatusshown in Figure 1; and

Figures 3 and 4 are each a detail elevational View, partly inyerticallongitudinal cross section.

of a portion of a modifled form of apparatus.

'I'he steel sheets which are to be coated are rst treated to remove dirtand scale, as, for

example, by pickling, blasting, etc. This step may be omitted if thesheets are originally clean.

The sheets are then treated in apparatus as shown in the drawing and.nowto be described.

Referring now more particularly. to Figures 1 f and v2, a set offeedrolls Ill'is located adjacent the entranceof a galya'nizing pot I I ofknown, construction and provided with entry guides I2 55 and feed rollsI3 by which sheets advancing through the feed rolls I0 are directeddownwardly into the pot II through a ux bath. I4 floating on the surfaceof the molten zinc or spelter contained in the pot II. Guides I5 directthe sheets 60 throughv the spelter between bottom rolls I6.

Guides I'I extend from the rolls I6 upwardly toward the exit rolls I8.'As the sheets pass between the rolls I8 they are engaged by exit guidesI9 which deliver them onto a conveyor 65- 20 or other transportingmeans.

When the form of apparatus shown in Figures 1 and 2 is used the sheetsare subjected to a mist or, very fine spray as they are l/carried alongby the conveyor 20. 'I'he mistor spray is'in- 70 dicated in Figure 1 byreference numeral 2| and is created kby means of very nely adjustedspray nozzles 22 connected 'with a supply of the fluid being sprayedvand a lsuitable source-of spraying pressure. The position of a sheet onthe conveyor is indicated at 23. With this form of apparatus the sprayimpinges on both sides of the sheet. The nozzles may, however, be sopositioned as to direct the spray against one or both sides ,of thesheet. The effect of the mist lor,

on various factors including the character and temperature of thespelter, ythe speed of movement of the sheet, the width.v and thicknessof the sheet, 'the weight of the coating,-the factor of whether the mistis applied to one or both sides of the sheet, etc. It is, however,important that the mist shall impinge upon the coated sheet before theprocess of vcrystallization has advanced A far enough so that theproduction of crystals clearly distinguishable to thel naked 'eye willresult. As crystallization may not set in immediately upon delivery of.the sheet from the spelter bath, particularly when a relatively heavycoating is applied, it is sometimes desirable not to treat thesuccessive portions of the coatedv sheet with the mist until apredetermined time after such portions have emerged from the spelter.

For example, a treatment such as that above described and illustrated inconnection with Fig` ures 1 and 2 allows a relatively great timeinterval before treatment of the sheets with the mist, although, ofcourse, the greater the speed of the sheets the greater the distancefrom 'the point .of emergence of the sheets from the spelter to thepoint of impingement of. the mist t ereon may be. f

Ihe apparatus shown in Figure, 3 is similar in all respects to thatshown in Figures 1 and 2 except for the positioning of the nozzles 24.These nozzles are arranged in two series extending transversely of 'sthesheet and substantially op- Dosite each other in the directionofmovement of the sheet, the nozzles being directed so that the mistimpinges on the sheet at an angle in the direction of movement of thesheet. It has been found that when the nozzles are so positionedsuperior results are obtained. The reason for this is not definitelyknown although. it is believed that when the nozzles are directed sothat the mist impinges on the sheet at an angle I `in the direction ofmovement of the sheet the Cil effect is to more rapidly evaporate themist particles without such a cooling eifect as will produce spangleswhich may result if the nozzles are directed so that the mist impingeson the sheet at an Iangle in the direction opposite the direction ofmovement of thesheet. "When it is desired to treat only one side of thesheet only one set of nozzles is operated, the other set being shut off.Alsoy in Figure 3'the nozzles are spaced nozzles 25 arepositioned so asto spray laterally from one or bothsides of the sheet, the sprayimpinging both on the sheet and also on the exit rolls I8. Anarrangement of this character is used on very thin sheets thinly coatedin which crystallization tends to commence immediately upon exposure ofthe coating to the air.

One important advantage of the invention is that y.the necessity forheating the treating substance is eliminated, together with theconsequent increased cost. Our treating substance ,may be applied atits. natural storage or room temperature and does not need to be heated.Apparently the very ne state of sub-division of the particles of themist prevents the mist from having an undesirable cooling effect whichmight tend to buckle the sheet. Furthermore, the resis'tance 'tocorrosion of the coated product does not appear to be substantiallylower than the does not', however, produce a product of the' characterin which weare interested. The effect t of a jet of dry steam is to wipethe coating, whileu the effect of a jet of wetsteam is to make thecoating brighter and more or less non-uniform.-

Also, a cooling air blast has been applied to galvanized sheets onemergence from a zinc bath,

but this treatment does not produce'the uniformv dull unspangled mattefinish which we produce but rather tends to increase the brightness andI Spangled effect' of the zinc coating. Our process monly termedspangles and thereafter vand while the coating is at least partiallymolten subjectlng the coating to an atomized liquid mist d the particleso'f which are -suiiiciently small to inhibit the propagation of crystalsvisible to Ath naked eye. i

2. In the manufacture of metal coated products, the steps comprisingapplying to a base a molten zinciferous coating such as would uponcooling normally form crystals of large size commonly termed "spanglesand thereafter and while the coating is at` least 4partially moltensubjecting tol the coating to an atomized mist of a solution of achemical which forms a minute precipitate at about the solidicationtemperature of the coatvsizecommonly termed "spangles and thereafter andwhile the coating is at least partially molten subjecting the coating totan atomized liquid mist the particles of which are sufficiently Ismallto inhibit thepropagation of crystals visible to the naked eye.

4. In the manufacture of coated metallic sheets.

the steps comprising applyingvto va base sheet a zinoiferous coatingsuch as would upon cooling normally form crystals of large size commonlytermed fspangles and thereafter and during the early stages ofcrystallization ofthe coating sub- 2,o94,5ss i -iecting the coating toan `atomized liquid mist the particles of `which are, sufficiently smalllto inhibit the propagation of crystalsvisible to the naked eye.

O. 6. Inthe manufacture of metal coated products, the steps comprisingpassing the metal to be .coated through a bath ofla molten zinciferous`vcoating ,material such as wouldupon cooling normally form crystals oflarge size commonly termed spangles whereby to coat the same andthereafter and while the coating is at least partially molten subjectingthe coating to an atomized liquid mist the particles 'of whichare'sufllciently small lto inhibit the propagation of crystals visibleto the naked eye.

' l l NELSON E. COOK.

EDWARD J. KNOPF.

WIT-11AM LDIEHL.

